PROJECT SUMMARY Mitochondria are dynamic organelles that continually move and re-shape through mitochondrial fusion and fission, two highly regulated processes that control mitochondrial morphology and ensure mitochondrial function, integrity and oxidative damage repair. Recently, the identity of some of the proteins involved in mitochondrial dynamics in mammalian cells has started to unveil. Mutations in genes encoding for some of these proteins have been shown to be responsible for several human diseases and cellular functions. In fact, mitochondrial dynamics and cell cycle are coupled, and the rate of fusion and fission is regulated during the different phases of the cell cycle, permitting appropriate phase progression and distribution of mitochondria in daughter cells during mitosis. Our group recently identified the polymerase delta interacting protein 2 (Poldip2) as a novel positive regulator of Nox4, and our new preliminary data suggest that Poldip2 controls the expression of the Mitochondria-Localized Glutamic Acid-Rich Protein (MGARP), a protein responsible for mitochondrial movement along the microtubules. These data raise the interesting possibility that Poldip2 participates in the regulation of mitochondrial movement and dynamics, and therefore cell bioenergetics. In this proposal, we will test the hypothesis that Poldip2 controls mitochondrial fission through the regulation of MGARP expression, which subsequently impacts cell cycle progression and proliferation. To address this problem, we will first determine the mechanism by which Poldip2 regulates mitochondrial dynamics. In the second aim, we will establish the functional consequences of Poldip2-mediated regulation of mitochondrial dynamics, focusing on mitochondrial damage repair and oxidative phosphorylation (OXPHOS) capacity and their impact in cell cycle progression. Because VSMC proliferation is known to be a critical component of atherosclerosis, our last aim will be devoted to investigating the role of the Poldip2/MGARP pathway in a model of partial ligation-induced atherosclerosis using inducible smooth muscle specific Poldip2 knockout mice on an ApoE-/- background. This research program will advance our understanding of the interface between mitochondrial dynamics and cell cycle progression, and will provide important insight into the role of two novel proteins in vascular pathology that may represent new targets for intervention.